Liquid set for ink jet recording

ABSTRACT

A liquid set for inkjet recording, includes (i) an aqueous treatment liquid including a polyurethane resin obtainable by reacting a polyester polyol, a diol containing a quaternary N-atom or tertiary amino group, and a polyisocyanate, wherein the quaternary N-atom or tertiary amino group is present in a side chain of the carbon chain linking the two hydroxyl groups of the diol, and the polyester polyol is obtained by reacting a polyol and an aromatic polycarboxylic acid; and (ii) an aqueous inkjet ink including a colorant. A method for inkjet printing includes using the liquid set.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage Application ofPCT/EP2018/082764, filed Nov. 28, 2018. This application claims thebenefit of European Application No. 17203985.1, filed Nov. 28, 2017,which is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a liquid set comprising a treatmentliquid comprising an aqueous polyurethane resin dispersion and anaqueous ink jet ink.

2. Description of the Related Art

In recent years, inkjet techniques have been increasingly utilized forindustrial printing applications such as displays, posters, bulletinboards, packaging, textile, etc. In such applications durability such aslight fastness, water resistance, and wear resistance are importantrequirements of the printed images and pigment based inks therefore havebeen developed.

Inks, such as solvent-based inkjet inks using an organic solvent as avehicle, and ultraviolet curable inkjet inks including a polymerisablemonomer as a main component have been used widely in industrialapplications.

However, the solvent-based inkjet inks are not environmentallypreferable because the solvent is evaporated in the atmosphere. Theultraviolet curable inkjet inks have limited application fields becausethey may have skin sensitizing properties depending on the monomer usedand an expensive ultraviolet irradiation apparatus is required to beincorporated to the main body of a printer.

In view of such background, there have been developed pigment basedaqueous inks for inkjet recording capable of being directly used forprinting on porous and non-porous substrates and which give lessenvironmental load. These inks are characterized by the presence of aresin which binds the pigments and prevents rubbing off the images fromthe substrate leading to an improved solvent and scratch resistance.

Usually, an ink-jet recording medium for aqueous ink jet inks includes asubstrate such as paper, a plastic film or textile fabric and an ink-jetreceiving layer provided thereon.

The layer is formed from an ink-jet receiving agent which mostlycontains a water soluble resin such as polyvinyl alcohol, polyvinylpyrrolidone and the like and any of various additives, in order toprevent bleeding and or ink coalescence caused by the water based ink orimprove ink absorbing property. Problems are caused because bleeding andcoalescence arises due to insufficient adsorption of the aqueous pigmentink into the ink-jet receiving layer.

Moreover, there is a problem that a printed image made by jettingaqueous ink jet inks has poor waterproof characteristics. The mostpopular method to improve the waterproof characteristics is a methodwherein an ink-jet receiving agent is used which includes an aqueouscationic resin such as a poly(diallyldimethylammonium chloride) inaddition to the aforementioned resin in the ink. Waterproofcharacteristics can be improved by fixing of the pigment of the aqueousink due to the electrostatic bonding between an anionic group of thepigment in the ink and a cationic group of the water-soluble cationicresin. However, since the water-soluble cationic resin itself tends tobe easily dissolved in water, the effect for improving waterproofcharacteristics was insufficient. Furthermore, these polymers do notcrosslink with each other nor form a film, leading to poor physicalproperties of the printed image.

WO14042652 discloses a fixer fluid to be used for making anink-receiving layer and comprising a liquid vehicle, a surfactant, and acationic polymer. The cationic polymer can be selected from the group ofquaternized polyamines, dicyandiamide polycations, diallyldimethylammonium chloride copolymers, quaternizeddimethylaminoethyl(meth)acrylate polymers, quaternized vinylimidizolpolymers, alkyl guanidine polymers, alkoxylated polyethylene imines.

JP2015163678A discloses an aqueous pigment composition for printing on aporous substrate such as textile which guarantees an improved washingfastness and rubbing resistance of the images on the fabric. The aqueouscomposition comprises pigment particles containing a urethane resinobtained by reacting polyester polyols with polyols comprising an ionicor non-ionic group and polyisocyanate.

US2009/0233065 discloses an ink jet pre-treatment liquid containing acationic polyurethane. The cationic polyurethane is obtained by makinguse of a chain extending agent having a tertiary amino group, hencebringing a cationic group in the main chain of the resin. The resinassures a good adhesion of the resin to non-porous substrates. Storagestability of the pre-treatment liquid containing the cationicpolyurethane is still to be improved.

US2008/0090949 discloses an ink-jet receiving agent including a cationicpolyurethane resin aqueous dispersion. The resin provides excellentwaterproof characteristics on a coating which is formed after removingwater from the dispersion. The tertiary amino group containing polyolhaving secondary OH-groups will have limited reactivity, limiting thelength of the polymer chains and hence reducing the physical propertiesof the resin such as adhesion, scratch resistance, and mechanicalperformance. Furthermore, the method of preparation of the cationicpolyurethane as disclosed in US2008/0090949 is laborious, since firstthe tertiary amino group containing polyol needs to be prepared inadvance. The incorporation of polyalkylene glycol units is limited intothe main chain of the polyurethane, which will lead to inferiorproperties with respect to colloidal stability of the aqueous resindispersion.

As described above, there is great need for the development of atreatment liquid of substrates for ink-jet printing with aqueous pigmentinks and which can provide an ink-jet receiving layer which is excellentin printing quality (colour density increase, coalescence and bleedingdecrease, fixing power) and which provides printed images showingexcellent physical properties (adhesion, waterproof characteristics,solvent resistance and flexibility) and which can be produced via anefficient synthesis method.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a solution for the abovestated problems. The object has been achieved by providing a liquid setas defined below and comprising a treatment liquid containing apolyurethane resin and an inkjet ink comprising a colorant.

According to another aspect, the present invention includes an inkjetrecording method using the polyurethane resin as defined below. Thismethod is also defined below.

Other features, elements, steps, characteristics and advantages of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments of the present invention. Specificembodiments of the invention are also defined below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A. Liquid Set forInkjet Recording

The liquid set for inkjet recording according to the invention comprisesan aqueous treatment liquid and an aqueous inkjet ink comprising acolorant.

A. 1. Aqueous Treatment Liquid

The aqueous treatment liquid from the liquid set according to thepresent invention contains a polyurethane resin as described in §A.1.1.1. and water. Additional components may be added to the treatmentliquid are given below. The amount of polyurethane resin in thetreatment liquid is equal to or lower than 30 wt. %.

A.1.1. Polyurethane Resin

The polyurethane resin incorporated in the treatment liquid of theliquid set of the present invention is characterised by the fact thatthe polyurethane resin comprises a cationic group in a side chain and apolyester. A polyalkylene oxide may also be present in a side chain ofthe polyester urethane backbone. Both the cationic group and thepolyalkylene oxide increase the dispersibility and colloidal stabilityof the resin in water. The polyester urethane resin of the invention isobtainable by reacting a polyester polyol containing aromatic moietieswith, a polyol containing a cationic group and a polyisocyanate.

A.1.1.1 Polyester Polyol

The polyester polyol used in the reaction of the invention, is obtainedby reacting an aromatic polycarboxylic acid and a polyol.

The polyester polyol is a resin formed by an esterification reaction ortransesterification reaction between at least one aromaticpolycarboxylic acid component and at least one polyol component.Specific examples of the aromatic polycarboxylic acid include dibasicacids such as phthalic acid, isophthalic acid, terephthalic acid,2,6-Naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid,1,5-naphthalenedicarboxylic acid; tri- or higher -valent polybasic acidssuch as trimellitic acid and pyromellitic acid; and acid anhydridesthereof, for example, phthalic anhydride, trimellitic anhydride,pyromellitic anhydride; and the like. As the aromatic polycarboxylicacid component, one or more dibasic acids selected from the dibasicacids mentioned above, lower alkyl ester compounds of these acids, andacid anhydrides are mainly used. If necessary, a monobasic acid such asbenzoic acid, crotonic acid or p-t-butyl benzoic acid; a tri- or highervalent polycarboxylic acid such as trimellitic anhydride,methylcyclohexene tricarboxylic acid or pyromellitic anhydride; or thelike can be further used in combination with the polycarboxylic acidcomponent. It is preferred that the polyester is prepared usingdicarboxylic acids which give linear polymer chains, in particular1,4-terephtalic acid copolymers give a better performance regardingcolloidal stability in aqueous medium, than phthalic acid anhydridecopolymers. Besides terephthalic acids, one could use also other para-or linear substituted polycarboxylic acids to obtain the desiredproperties such as 2,6-naphthalenedicarboxylic acid or1,5-naphthalenedicarboxylic acid.

The preferred carboxylic acid is an aromatic dicarboxylic acid such asterephthalic acid and isophthalic acid. The content of aromatic acidswithin the resin is equal to or higher than 30 mol % and preferablyequal to or higher than 50 mol % with respect to the total amount ofdicarboxylic acids or anhydrides. Treatment liquids comprisingpolyurethane resins obtained by reaction of polyesters polyolscontaining aromatic polycarboxylic acids do show an improved colloidalstability and lead to images with an improved solvent resistance and animproved dry and wet scratch resistance. The good results obtained withterephthalic acids and isophthalic acids has probably to do withobtaining a certain amount of crystallinity of the polyurethane resin orproviding linear amorphous chains which contribute more to the desiredphysical properties such as scratch resistance and solvent resistance.Introducing phthalic acid anhydride or isophthalic acid in terephthalicacid based polyesters reduces the crystallinity or chain end-to-enddistance and improves the solubility in organic solvents. Forterephthalic acid based polyester polyols, it is preferred to usecopolymers of terephthalic acid with isophthalic acid, more preferablyhaving at least 20 mol % isophthalic acid. For the same reason polyesterpolyols with only phthalic acid anhydride are less preferred thancopolymers where terephthalic acid is incorporated. Polyester polyolsbased on only phtalic acid anhydride could be very soluble in thepolymerization solvent for the PU preparation, but a dried coating willhave also a lower solvent resistance. Therefore, it is preferred thatthe aromatic polyester polyol contains between 20 and 80 mol % ofterephthalate groups on the basis of the total amount of dicarboxylicacids (or acid anhydrides) in the polyester polyol.

Very suitable polyester polyols containing terephthalic ester units andisophthalic ester units in a ratio of 1:1 mol % are: Dynacoll 7150supplied by Evonik, Marl, Germany, Vylon 220 from Toyobo, Osaka Japanand Elitel 1401 obtained from Unitika Ltd Dusseldorf Germany.

In order to obtain the desired properties of the polyester polyol andusing a high content of terephthalic acid, one could use also a mixtureof dicarboxylic acids. For example, to reduce the crystallinity onecould use a mixture of terephthalic acid and adipic acid. Consequently,one could use also polyester polyols based on a mixture of aromaticpolycarboxylic acids and aliphatic dicarboxylic acids such as adipicacid, succinic acid, methylcyclohexene tricarboxylic acid, fumaric acidand sebacic acid or anhydrides such as tetrahydrophthalic acidanhydride, hexahydrophtalic acid anhydride, maleic acid anhydride andsuccinic acid anhydride.

Polyester polyols with a high content of terephthalic acid could have apoor solubility in the preparation solvent (e.g. acetone) for the PUpreparation or could have a too high degree of crystallinity in order toget good adhesive properties. In particular, this is the case when onlynon-branched diols are used for the polyester polyol, such as1,2-ethylene glycol or 1,4-butane diol. When using terephthalic acidbased polyester polyols with more than 35 mol % terephthalic acid, onecan preferably use a mixture of different non-branched diols (e.g. amixture of 1,2-ethylene glycol and 1,4-butane diol) or a mixture of anon-branched diol (e.g. ethylene glycol) with a branched diol (e.g.neopentyl glycol). When using mixtures of different diols for thepolyester polyol, one could use high terephthalic acid contents, even upto 100 mol % based of the total dicarboxylic acid content.

Specific examples of the polyol component include diols such as ethyleneglycol, diethylene glycol, propylene glycol, dipropylene glycol,1,4-butanediol, neopentyl glycol, 1,5-pentanediol,3-methyl-1,5-pentanediol, 1,4-hexanediol and 1,6-hexanediol; and tri- orhigher-valent polyols such as glycerin, trimethylolethane,trimethylolpropane and pentaerythritol. For the polyol component, diolsas mentioned above are mainly used, and if necessary, tri- orhigher-valent polyols such as glycerin, trimethylolethane,trimethylolpropane and pentaerythritol can be further used incombination with the diols. Aromatic diols can also be used to increasethe content of aromatic moieties in the polyester polyol. Suitablearomatic diols are: p-xylene glycol, 1,5-naphthalenedimethanol,1,4-naphthalenedimethanol, 4,4′-bis(hydroxymethyl)biphenyl,bis(hydroxyethyl) terephthalate, bis(2-hydroxypropyl) terephthalate,1,5-naphthalenedicarboxylic acid 1,5-bis(2-hydroxyethyl) ester,4,4-bis(hydroxymethyl) diphenylmethane,2,2-bis(4-β-hydroxyethoxyphenyl)propane (diethoxylated bisphenol A) andbis[p-(2-hydroxyethoxy)phenyl]methane.

Preferably diols with a Mw equal to or less than 400 are used togetherwith the polyester polyol. These polyols can be used singly or asmixture of two or more kinds.

A.1.1.2. Diols Containing an Amino Group or Cationic Group

Examples of the cationic group in the polyurethane resin of theinvention can be selected from protonated amines, protonated nitrogencontaining heteroarmoatic compounds, quaternized tertiary amines,N-quaternized heteroaromatic compounds, sulfoniums and phosphoniums,quaternized tertiary amines and N-quaternized heteroaromatic compoundsbeing more preferred.

The diol to be used for obtaining the polyurethane resin of theinvention contains a quaternary N-atom or amino group, the quaternaryN-atom or tertiary amino group being present in a side chain beingpresent in the side chain of the carbon chain linking the two hydroxylgroups of the diol, hence not present in the carbon chain between thetwo hydroxyl groups of the diol.

Preferably a diol is used containing an amino group, preferably atertiary amino group, ie a precursor for obtaining a cationic groupafter protonation using an acid, e.g. acetic acid. The amino group andmore preferably the tertiary amino group is not present in the chainbetween the two hydroxygroups of the diol. Hence the amino group andmore preferably the tertiary amino group or quaternary ammonium group ispresent in the side chain of the prepared polyurethane resin. Afterpreparation of the polyurethane in a solvent like acetone, the aminogroup and preferably tertiary amino group is converted to a quaternaryammonium group by protonation with an acid, e.g. acetic acid.Subsequently water is added during a high shear treatment or stirring toobtain an aqueous dispersion. Subsequently the organic solvent (e.g.acetone) is removed by distillation under reduced pressure.

Examples of suitable diols having a N-atom in the side chain forintroducing a cationic group in the resin are:2-[(Dimethylamino)methyl]-1,3-propanediol, CAS Registry Number69040-18-2, 2-Methyl-2-dimethylaminomethyl-1,3-propanediol, CAS RegistryNumber 36254-31-6, 2-Ethyl-2-dimethylaminomethyl-1,3-propanediol, CASRegistry Number 25941-41-7, 2-Diethylaminoethyl-2-methyl-1,3-propanediol, CAS Registry Number 29006-31-3 ,2-Diethylaminomethyl-2-ethyl-1,3-propanediol, CAS Registry Number26102-95-4, 3-[methyl(phenylmethyl)amino]- 1,2-propanediol, CAS RegistryNumber 60278-98-0. Diols having a N-atom in the side chain have theadvantage that the colloidal stabilisation of the produced polyurethaneresin is further improved with respect to the diols having a N-atom inthe main chain.

When using a tertiary amino group containing diol, the amino group isconverted to a cationic group by protonation using an inorganic ororganic acid. Examples of inorganic acids are hydrochloric acid,perchloric acid, sulphuric acid, hydrobromic acid, hydroiodic acid,phosphoric acid, nitric acid, boric acid, etc. Examples of organic acidsinclude: acetic acid, formic acid, propionic acid, citric acid, oxalicacid, ascorbic acid, lactic acid, benzoic acid, toluene sulphonic acid,phenol, salicylic acid, acrylic acid, maleic acid, itaconic acid,stearic acid, glutamic acid, sulfoethyl methacrylate, carboxyethylacrylate 2-acrylamido-2-methyl-1-propanesulfonic acid,monoacryloyloxyethyl hexahydrophthalate, methacryloyloxyethyl succinate,acryloyloxyethyl succinate or other organic compounds with an acidicproton such as sulphonamides or thiols.

Other examples of quaternary amines are[p-(2,3-Dihydroxypropoxy)phenyl]trimethylammonium bromide=CAS regsirynumber 109732-00-5, [m-(2,3-Dihydroxypropoxy)phenyl] trimethylammoniumbromide=CAS registry number 109731-98-8,[2-[p-(2,3-Dihydroxypropoxy)phenoxy] ethyl]trimethylammonium iodide =CASregistry number 110056-43-4 and quarternary amino diols having thequarternary amino group in the side chain, e.g. 2,3-Dihydroxy-N,N,N-trimethyl-1-propanaminium=CAS registry number 44814-66-6.

In a further preferred embodiment, the diol having an amino group3-(Dimethylamino)-1,2-propanediol.

A.1.1.3. Polyether Diol

The polyether diol which can be used in the present invention can beobtained by addition polymerization of an alkylene oxide with at leastone compound having two or more active hydrogen atoms. Examples of thiscompound include ethylene glycol, diethylene glycol, triethylene glycol,propylene glycol, trimethylene glycol, 1,3-butanediol, 1,4-butanediol,1,6-hexanediol, glycerol, trimethylolethane and ethylolpropane. Examplesof the alkylene oxide include ethylene oxide, propylene oxide, butyleneoxide, styrene oxide, epichlorohydrin and tetrahydrofuran. Preferredpolyether diols are compounds according to Formula 1.

wherein R1 is methyl or ethyl, R2 is H or C₁-C₄ alkyl and n representsan integer from 5 to 50, more preferably from 10 to 40 and mostpreferably from 15 to 30.

The polyether diol which can be preferably used in the presentinvention, is Ymer N120 or Tegomer D 3403, i.e. α-[2,2-bis(hydroxymethyl)butyl]-ω-methoxy-Poly(oxy-1,2-ethanediyl). These diolscan be prepared from trimethylol propane oxetane (TMPO). A possiblesynthesis procedure is described by Fock, J.; Möhring, V.,Polyether-1,2- and -1,3-diols as macromonomers for the synthesis ofgraft copolymers, 1. Synthesis and characterization of themacromonomers. Die Makromolekulare Chemie 1990, 191 (12), 3045-3057.

In general also other polyether 1,2- or 1,3-diols can be used. For agood stability the polyether graft needs to be well water soluble inorder to give a good steric stabilisation. In the case of Ymer N120 thepolyether is only composed of ethylene oxide segments, but this can alsobe a copolymer of different alkylene oxides. Furthermore in the currentmacro-monomer diol the end group is a methoxy group, this end group canalso be other end groups such as a hydrophilic end group (such asanionic groups, e.g. carboxylic, sulphate, phosphate, etc. or cationicgroups, e.g. quaternary amine groups or precursors for cationic groupse.g. tertiary amino groups) in order to have also electro-stericstabilisation. The content of the polyether diol in the polyurethaneresin is preferably 30 wt. % or less, but more than 1 wt. % with respectto the total solid weight of the polyurethane resin, more preferably thepolyether diol content is equal to or less than 15 wt. % and more than 2wt. % with respect to the polyurethane resin. A content of the polyetherdiol of less than 30 wt. %, but more than 1 wt. % with respect to thepolyurethane resin, has an additional improvement in scratch resistanceand solvent resistance of the jetted and dried image with respect topolyether diol content outside this range. Too high polyether diolcontent (more than 30 wt %) would lead to a too high water solubilityand lower glass transition temperature.

A.1.1.4. Polyisocyanates

Specific examples of the organic polyisocyanate compound that is reactedwith the polyester polyol include aliphatic diisocyanates such as lysinediisocyanate, hexamethylene diisocyanate and trimethylhexanediisocyanate; cyclic aliphatic diisocyanates such as hydrogenated xylenediisocyanate, isophorone diisocyanate, methylcyclohexane-2, 4 (or2,6)-diisocyanate, 4,4′-methylenebis(cyclohexyl isocyanate) and1,3-(isocyanatomethyl)cyclohexane; aromatic diisocyanates such astolylene diisocyanate, xylene diisocyanate and diphenylmethanediisocyanate; organic polyisocyanates themselves, including tri- orhigher-valent polyisocyanates such as lysine triisocyanate; adducts eachcomposed of such an organic polyisocyanate with a polyhydric alcohol, alow molecular weight polyester resin or hydrogen; and cyclised polymers(for example, isocyanurate), biuret type adducts and the like, eachformed from various diisocyanate compounds mentioned above.

It is preferable, from the viewpoint of storage stability of thetreatment liquid composition, that the organic polyisocyanate compoundaccording to the invention include at least one selected fromnon-yellowing type polyisocyanate compounds such as isophoronediisocyanate, hexamethylene diisocyanate and lysine diisocyanate, and itis more preferable that the organic polyisocyanate compound include atleast isophorone diisocyanate.

Furthermore, the organic polyisocyanate compounds can be used singlyalone or as mixtures of two or more kinds.

A.1.1.5. Reaction Conditions

With regard to the conditions for the reaction between the polyesterpolyol, the polyol containing a cationic group and the organicpolyisocyanate compound, those conventionally used reaction conditionscan be used without particular limitation.

Besides the preferred terephthalate containing polyester polyols also amixture of different polymeric polyols can be used to adjust thephysical properties, adhesion, mechanical performance, etc. Examples aree.g. polycarbonate polyols, polyether polyols, polyacrylate polyols,aliphatic polyester polyols, polyolefin polyols or other polymericpolyols. Examples of polycarbonate polyols are e.g. Oxymer C112, OxymerM112 (available via Perstorp), Kuraray polyol C-2050, C-2090, C-1090(available from Kuraray), Converge HMA-1 and Converge HMA-1 (availablefrom Novomer Inc.), Duranol T6002, T6001, T5652, T5651, T5650J, T4672,T4671, T4692 and T4691 (available from Asahi kasei). Additionalaliphatic polyester polyols, are e.g. regular (semi)crystalline oramorphous grades, e.g. based on hexane diol adipates (e.g. Dynacoll 7372from Evonik) but also polyester polyols based on natural products suchas polyester polyols made by using dimer acid or dimer diols (e.g. tradename Priplast from Croda), examples are Priplast 3192 and Priplast 1838.The raw material used to prepare certain Priplast grades, i.e. dimerdiols with trade name Pripol can also be used as monomer in the PUsynthesis to modify the physical properties and adhesive properties.

In the reaction between the polyester polyol and the organicpolyisocyanate compound, if necessary, a diol with Mw equal to or lessthan 400 can be used. Examples of suitable diols are: ethylene glycol,diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol,neopentyl glycol, 1,5-pentanediol, 3-methyl-1,5-pentanediol,1,4-hexanediol and 1,6-hexanediol; and tri- or higher-valent polyolssuch as glycerin, trimethylolethane, trimethylolpropane andpentaerythritol. 1,4-butane diol is most preferred.

In the polyurethane synthesis different high molar mass polyols and lowmolecular weight diols can be reacted, besides the polyether diols usedfor stabilization of the polyurethane dispersion. In the procedure used,the stabilizing polyols and the polyester polyol (Mw>400 g/mol) arereacted with in excess of isocyanate. This enables a good conversion ofthe reaction. Depending on the molecular weight and the copolymercomposition, the polyester polyol, may have a poor solubility in thereaction solvent (e.g. acetone). Also the polyol with the anionic grouphas a poor solubility in acetone. After reacting using an excess ofisocyanate, the excess is compensated to a NCO/OH molar ratio byaddition of a low molecular weight diol, which would lead to apolyurethane resin with very low amount of residual isocyanate. In casesome residual isocyanate is present some urea bonds could be formed.Examples of suitable diols are given above.

So in the reaction conditions used a pre-condensation step withNCO/OH-ratio>1 and a chain extension step at NCO/OH-ratio =1.0 can bedistinguished. Instead of using a 2-step process, one could use also aone-step or semi-continuous process. In the 2-step process, when using ahigh NCO/OH ratio more low molar mass diol (chain extender) is added andthe weight ratio of the polyester polyol is reduced. In order to obtainthe desired properties, the amount of polyester polyol as compared tolow molar mass diols should be considerably higher, i.e. at least 50 wt.%. Surprisingly it was found that upon using high NCO/OH ratios in thepre-condensation step this resulted into polyurethane dispersions withpoorer colloidal stability because of more coarse particles leading toan ink jet ink having poorer filterability. Reacting at a higher NCO/OHratio in the pre-condensation step will lead also to a higher content ofurethane units, which are able to form hydrogen bonds. When keeping thetype of polyester polyol constant and also the chain extender, reactingat an NCO/OH ratio more close to NCO/OH=1.0, leads to better colloidalstability and better filtration properties of the formulated ink jetink. Consequently when the NCO/OH ratio and the amount of urethane bondsplay an important role, also the molecular weight of the polyesterpolyol and the low molar mass diol plays a role. In the most examplesonly one polyester polyol is used and only one low molar mass diol. Whenusing mixtures of diols one can easily calculate the number averagemolecular weight which will affect the NCO/OH ratio.

Examples of the organic solvent used for the reaction between thepolyester polyol, the polyether diol, the polyol comprising a cationicgroup and the organic polyisocyanate compound, here include ketones suchas acetone and methyl ethyl ketone, ethers such as tetrahydrofuran anddioxane, acetates such as ethyl acetate and butyl acetate, nitriles suchas acetonitrile, and amides such as dimethyl formamide,N-methylpyrrolidone and N-ethylpyrrolidone. These may be used singly orin combinations of two or more.

Using higher molecular weight polyols than Ymer120N will give more phaseseparation, providing a better water dispersibility. However, for themaking of the polyurethane resin, it is more difficult to dissolve thesepolyols in de organic solvent, e.g. acetone. This can be overcome byusing a co-solvent during the polycondensation reaction. A preferredco-solvent is 2-pyrolidon or N-methylpyrrolidone, more preferably2-pyrolidon.

The treatment liquid composition of the invention contains thepolyurethane resin as an essential component. Therefore, thepolyurethane resin is preferably dispersed in water to obtain an aqueousdispersion of the polyurethane resin. Every dispersing technologysuitable for preparing an aqueous dispersion may be used.

A.1.2. Water Soluble Organic Solvent

The treatment liquid of the invention may contain, besides water as asolvent, also a water-soluble organic solvent. Examples of water-solubleorganic solvents include polyhydric alcohols such as diethylene glycol,triethylene glycol, dipropylene glycol, 1,3-propanediol, 1,3-butanediol,1,4-butanediol, 2,2-dimethyl-1, 3-propanediol, 2-methyl-1,3-propanediol, 1,2-pentanediol, 2,4-pentanediol, 1,5-pentanediol1,6-hexanediol, 2-ethyl-1, 3-hexanediol, 1,2-hexanediol and2,5-hexanediol, polyhydric alcohol alkyl ethers such as dipropyleneglycol n-propyl ether, tripropylene glycol methyl ether, tripropyleneglycol n-propyl ether, propylene glycol phenyl ether, triethylene glycolmethyl ether, triethylene glycol methyl ether, triethylene glycol ethylether, diethylene glycol n-hexyl ether and ethylene glycol phenyl ether,and nitrogen-containing heterocyclic compounds such as 2-pyrrolidone andN-methylpyrrolidone.

Other preferred water soluble organic solvents include ethylene glycol,propylene glycol, 1,2-butanediol, 2,3-butanediol, 2-methyl-2,4-pentanediol, dipropylene glycol monomethyl ether, propylene glycoln-butyl ether, propylene glycol t-butyl ether, diethylene glycol methylether, ethylene glycol n-propyl ether and ethylene glycol n-butyl ether.

The content of the water-soluble organic solvent, in the aqueous ink jetink is preferably less than 70 wt. %. If the content exceeds 70% bymass, the ink loses its water based, hence more green character.

A.1.3. Surfactant

In the treatment liquid of the present invention, a surfactant may beadded in order to ensure wettability onto the substrate. The amount ofthe surfactant added is preferably 0.1 wt. % to 5 wt. % as an activecomponent in the ink.

If the amount added is below 0.1% by mass, wettability onto thesubstrate is not sufficient and causes degradation in image quality andin adhesion to the substrate. The surfactant that can be used is notparticularly limited as long as it satisfies the above limitation.

While any of an amphoteric surfactant, a non-ionic surfactant, or acationic surfactant can be used, non-ionic surfactants such aspolyoxyethylene alkyl phenyl ether, polyoxyethylene alkyl ester,polyoxyethylene alkylamine, polyoxyethylene alkyl amide, apolyoxyethylene propylene block polymer, sorbitan fatty acid ester,polyoxyethylene sorbitan fatty acid ester and an ethylene oxide adductof acetylene alcohol are preferably used in terms of a relationshipbetween dispersing stability and image quality. In addition, afluorine-based surfactant and a silicon-based surfactant can be used incombination (or singly) depending on formulation.

Suitable surfactants are siloxane based surfactants such as Tego Twin4000 from Evonik Industries, Tegowet 270 from Evonik industries,Hydropalat WE3220 from BASF, silane based surfactants such as SilwetHS312 from Momentive and fluor containing surfactants such as: ThetawetFS8150 from Neochem GMBH, Capstone FS3100 from Dupont, Tivida FL2500from Merck and surfactants from the Dynol, Envirogem & Surfynol seriesfrom Air products.

A.1.4. Additives

Together with the polyurethane resin, a multivalent metal ion can becontained in the treatment liquid. Suitable examples are water-solublemetal salts formed from bi- or higher valent metal cations, such asmagnesium, calcium, strontium, barium, zirconium, and aluminum, andanions, such as a fluoride ion (F⁻), a chloride ion (Cl⁻), a bromide ion(Br⁻) , a sulfate ion (SO₄ ²⁻, a nitrate ion (NO₃ ⁻, and an acetate ion(CH₃COO⁻).

These polyvalent metal ions have a function of aggregating ink by actingon anionic groups such as the carboxyl groups on the surface of thepigment or the dispersed polymer of capsules contained in the ink. As aresult, the ink remains on the surface of the substrate to improve thecolour-developing property. Therefore, it is preferred that the surfaceof the pigment in the ink and/or the dispersed polymer of the capsulescontained in the ink have an anionic group selected from the group ofcarboxyl group, sulfonate group and phosphonate group, most preferablycarboxyl group.

The treatment liquid may also contain organic acids. Preferred examplesof the organic acids include, but are not limited to acetic acid,propionic acid, and lactic acid.

The treatment liquid may also contain colorants, such as pigments.Particularly useful for printing on dark substrates is a treatmentliquid containing a white pigment. The preferred pigment for the aqueoustreatment liquid ink is titanium dioxide. Titanium dioxide (TIO₂)pigment useful in the present invention may be in the rutile or anatasecrystalline form. Processes for making TiO₂ are described in greaterdetail in “The Pigment Handbook”, Vol. I, 2nd Ed., John Wiley & Sons,N.Y. (1988), the relevant disclosure of which is incorporated byreference herein for all purposes as if fully setforth.

The titanium dioxide particles can have a wide variety of averageparticle sizes of about 1 micron or less, depending on the desired enduse application of the treatment liquid. For applications demanding highhiding or decorative printing applications, the titanium dioxideparticles preferably have an average size of less than about I μm.Preferably, the particles have an average size of from about 50 to about950 nm, more preferably from about 75 to about 750 nm, and still morepreferably from about 100 to about 500 nm.

In addition, unique advantages may be realized with multiple particlesizes, such as opaqueness and UV protection. These multiple sizes can beachieved by adding both a pigmentary and a nano grade of TIO₂.

The titanium dioxide pigment may also bear one or more metal oxidesurface coatings. These coatings may be applied using techniques knownby those skilled in the art. Examples of metal oxide coatings includesilica, alumina, aluminasilica, boria and zirconia, among others. Thesecoatings can provide improved properties including reducing thephotoreactivity of the titanium dioxide. Metal oxide coatings ofalumina, aluminasilica, boria and zirconia result in a positive chargedsurface of the TiO₂ pigments and hence are particularly useful incombination with the cationic stabilised capsules of the inventionbecause no additional surface treatment of the pigment is required.

Commercial examples of such coated titanium dioxides include R700(alumina-coated, available from E. I. DuPont deNemours, WilmingtonDel.), RDI-S (alumina-coated, available from Kemira IndustrialChemicals, Helsinki, Finland), R706 (available from DuPont, WilmingtonDel.) and W-6042 (a silica alumina treated nano grade titanium dioxidefrom Tayco Corporation, Osaka Japan). Other suitable white pigments aregiven by Table 2 in [0116] of WO 2008/074548. The white pigment ispreferably a pigment with a refractive index greater than 1.60. Thewhite pigments may be employed singly or in combination. Preferablytitanium dioxide is used as pigment with a refractive index greater than1.60. Suitable titanium dioxide pigments are those disclosed in [0117]and in [0118] of WO 2008/074548.

A.2. Ink Jet Ink Composition

The liquid set according to the invention further comprises an aqueousinkjet ink comprising a colorant.

A.2.1. Solvent

The aqueous medium of the ink contains water, but may preferably includeone or more water-soluble organic solvents. The one or more organicsolvents may be added for a variety of reasons. For example, it can beadvantageous to add a small amount of an organic solvent to improve thedissolution of a compound in the inkjet ink to be prepared. Preferablewater-soluble organic solvents are polyols (e.g., ethylene glycol,glycerin, 2-ethyl-2-(hydroxymethyl)-1,3-propanediol, tetraethyleneglycol, triethylene glycol, tripropylene glycol, 1,2,4-butanetriol,diethylene glycol, propylene glycol, dipropylene glycol, butyleneglycol,1 ,6-hexanediol, 1 ,2-hexanediol, 1 ,5-pentanediol, 1,2-pentanediol,2,2-dimethyl-1 ,3-prapanediol, 2-methyl-2,4-pentanediol, 3-methyl-1,5-pentanediol, 3-methyl-1 ,3-butanediol, and 2-methyl-1,3-propanediol), amines (e.g., ethanolamine, and 2-(dimethylamino)ethanol), monohydric alcohols (e.g., methanol, ethanol, and butanol),alkyl ethers of polyhydric alcohols (e.g., diethylene glycol monomethylether, diethylene glycol monobutyl ether, triethylene glycol monomethylether, triethylene glycol monobutyl ether, ethylene glycol monomethylether, ethylene glycol monobutyl ether, propylene glycol monomethylether, propylene glycol monobutyl ether, and dipropylene glycolmonomethyl ether), 2,2′-thiodiethanol, amides (e.g.,N,N-dimethylformamide), heterocycles (e.g., 2-pyrrolidone andN-methyl-2-pyrrolidone), and acetonitrile.

A.2.2. Colorants

The colorants which can be included in the ink jet ink can be dyes orpigments.

The pigments may be black, white, cyan, magenta, yellow, red, orange,violet, blue, green, brown, mixtures thereof, and the like. A colourpigment may be chosen from those disclosed by HERBST, Willy, et al.Industrial Organic Pigments, Production, Properties, Applications. 3rdedition. Wiley- VCH, 2004. ISBN 3527305769.

Suitable pigments for use in the ink jet ink of the invention aredisclosed in paragraphs [0128] to [0138] of WO 2008/074548. The pigmentparticles are dispersed in an aqueous medium using a polymericdispersant, a (anionic) surfactant, but preferably a self-dispersiblepigment is used. The latter prevents interaction of the polymericdispersant with the dispersing groups of resin particles of theinvention which may be included in the inkjet ink (see below), sincedispersion stability of the pigment is accomplished by the sametechnique of electrostatic stabilization as employed for the resinparticles.

A self-dispersible pigment is a pigment having on its surface covalentlybonded anionic hydrophilic groups, such as salt-forming groups or thesame groups used as dispersing groups for the resin particles, thatallow the pigment to be dispersed in an aqueous medium without using asurfactant or a resin.

The technology for making self-dispersible pigments is well-known. Forexample, EP1220879A discloses pigments having attached a) at least onesteric group and b) at least one organic ionic group and at least oneamphiphilic counterion, wherein the amphiphilic counterion has a chargeopposite to that of the organic ionic group that are suitable for inkjetinks. Also EP906371A discloses suitable surface-modified colouredpigment having attached hydrophilic organic groups containing one ormore ionic groups or ionizable groups. Suitable commercially availableself-dispersible colour pigments are, for example, the CAB-O-JET™ inkjetcolorants from CABOT.

Pigment particles in inkjet inks should be sufficiently small to permitfree flow of the ink through the inkjet-printing device, especially atthe ejecting nozzles. It is also desirable to use small particles formaximum colour strength and to slow down sedimentation.

The average pigment particle size is preferably between 0.050 and 1 μm,more preferably between 0.070 and 0.300 μm and particularly preferablybetween 0.080 and 0.200 μm. Most preferably, the numeric average pigmentparticle size is no larger than 0.150 μm. The average particle size ofpigment particles is determined with a Brookhaven Instruments ParticleSizer BI90plus based upon the principle of dynamic light scattering. Theink is diluted with ethyl acetate to a pigment concentration of 0.002 wt%. The measurement settings of the BI90plus are: 5 runs at 23° C., angleof 90° , wavelength of 635 nm and graphics=correction function.

However, for white pigment inkjet inks, the numeric average particlediameter of the white pigment is from about 50 to about 950 nm, morepreferably from about 75 to about 750 nm, and still more preferably fromabout 100 to about 500 nm.

Suitable white pigments are given by Table 2 in [0116] of WO2008/074548. The white pigment is preferably a pigment with a refractiveindex greater than 1.60. The white pigments may be employed singly or incombination. Preferably titanium dioxide is used as pigment with arefractive index greater than 1.60. Suitable titanium dioxide pigmentsare those disclosed in [0117] and in [0118] of WO 2008/074548. Alsospecial colorants may be used, such as fluorescent pigments for specialeffects in clothing, and metallic pigments for printing a luxury look ofsilver and gold colours on textiles.

Suitable polymeric dispersants for the pigments are copolymers of twomonomers but they may contain three, four, five or even more monomers.The properties of polymeric dispersants depend on both the nature of themonomers and their distribution in the polymer. Copolymeric dispersantspreferably have the following polymer compositions:

statistically polymerized monomers (e.g. monomers A and B polymerizedinto ABBAABAB);

alternating polymerized monomers (e.g. monomers A and B polymerized intoABABABAB);

gradient (tapered) polymerized monomers (e.g. monomers A and Bpolymerized into AAABAABBABBB);

block copolymers (e.g. monomers A and B polymerized into AAAAABBBBBB)wherein the block length of each of the blocks (2, 3, 4, 5 or even more)is important for the dispersion capability of the polymeric dispersant;

graft copolymers (graft copolymers consist of a polymeric backbone withpolymeric side chains attached to the backbone); and

mixed forms of these polymers, e.g. blocky gradient copolymers.

Suitable dispersants are DISPERBYK™ dispersants available from BYKCHEMIE, JONCRYL™ dispersants available from JOHNSON POLYMERS andSOLSPERSE™ dispersants available from ZENECA. A detailed list ofnon-polymeric as well as some polymeric dispersants is disclosed by MCCUTCHEON. Functional Materials, North American Edition. Glen Rock, N.J.:Manufacturing Confectioner Publishing Co., 1990. p.110-129.

The polymeric dispersant has preferably a number average molecularweight Mn between 500 and 30000, more preferably between 1500 and10000.The polymeric dispersant has preferably a weight average molecularweight Mw smaller than 100,000, more preferably smaller than 50,000 andmost preferably smaller than 30,000.

The pigments are preferably present in the range of 0.01 to 20%, morepreferably in the range of 0.05 to 10% by weight and most preferably inthe range of 0.1 to 5% by weight, each based on the total weight of theinkjet ink. For white inkjet inks, the white pigment is preferablypresent in an amount of 3% to 40% by weight of the inkjet ink, and morepreferably 5% to 35%. An amount of less than 3% by weight cannot achievesufficient covering power.

A.2.3. Resin

The ink jet ink composition according to the invention may furthercomprise an additional resin. The resin is often added to the ink jetink formulation to achieve a good adhesion of the pigment to thesubstrate such as the fibres of the textile fabric. The resin is apolymer and suitable resins can be acrylic based resins, aurethane-modified polyester resin or a polyethylene wax, more preferablya urethane-modified polyester resin.

The polyurethane resin is to be incorporated in the ink formulation as adispersion and may be selected from the group consisting of aliphaticpolyurethane dispersions, aromatic polyurethane dispersions, anionicpolyurethane dispersions, non-ionic polyurethane dispersions, aliphaticpolyester polyurethane dispersions, aliphatic polycarbonate polyurethanedispersions, aliphatic acrylic modified polyurethane dispersions,aromatic polyester polyurethane dispersions, aromatic polycarbonatepolyurethane dispersions, aromatic acrylic modified polyurethanedispersions, for example, or a combination of two or more of the above.

A preferred urethane resin to be used as dispersion in the ink of theinvention is a polyester resin including a structural unit containing aurethane bond. Among such resins, a water-soluble or water-dispersibleurethane-modified polyester resin is preferred. It is preferable thatthe urethane-modified polyester resin include at least one structuralunit derived from a hydroxyl group-containing polyester resin (polyesterpolyol) and at least one structural unit derived from an organicpolyisocyanate.

Furthermore, the hydroxyl group-containing polyester resin is a resinformed by an esterification reaction or transesterification reactionbetween at least one polybasic acid component and at least onepolyhydric alcohol component.

A preferred polyurethane resin to be included in the ink of theinvention is a polyurethane resin obtainable by reacting a polyesterpolyol, a polyether diol, a polyol containing an anionic group and apolyisocyanate. A particular preferred polyurethane resin is apolyurethane resin obtainable by reacting a polyester polyol, apolyether diol, a polyol containing an anionic group and apolyisocyanate, and wherein the polyester polyol is obtained by reactingan aromatic polycarboxylic acid and a polyol. Examples of suitablepolyurethane resins and their preparations are disclosed in theunpublished patent application EP16196224.6.

Some examples of suitable polyurethane dispersions are NEOREZ R-989,NEOREZ R-2005, and NEOREZ R-4000 (DSM NeoResins); BAYHYDROL UH 2606,BAYHYDROL UH XP 2719, BAYHYDROL UH XP 2648, and BAYHYDROL UA XP 2631(Bayer Material Science); DAOTAN VTW 1262/35WA, DAOTAN VTW 1265/36WA,DAOTAN VTW 1267/36WA, DAOTAN VTW 6421/42WA, DAOTAN VTW 6462/36WA (CytecEngineered Materials Inc., Anaheim Calif.); and SANCURE 2715, SANCURE20041, SANCURE 2725 (Lubrizol Corporation), for example, or acombination of two or more of the above.

Acrylic based resins include polymers of acrylic monomers, polymers ofmethacrylic monomers, and copolymers of the aforementioned monomers withother monomers. These resins are present as a suspension of particleshaving an average diameter of about 30 nm to about 300 nm. The acryliclatex polymer is formed from acrylic monomers or methacrylic monomerresidues. Examples of monomers of the acrylic latex polymer include, byway of illustration, acrylic monomers, such as, for example, acrylateesters, acrylamides, and acrylic acids, and methacrylic monomers, suchas, for example, methacrylate esters, methacrylamides, and methacrylicacids. The acrylic latex polymer may be a homopolymer or copolymer of anacrylic monomer and another monomer such as, for example, a vinylaromatic monomer including, but not limited to, styrene, styrenebutadiene, p-chloromethylstyrene, divinyl benzene, vinyl naphthalene anddivinylnaphthalene.

Some examples of suitable acrylic latex polymer suspensions are, JONCRYL537 and JONCRYL 538 (BASF Corporation, Port ArthurTX); CARBOSET GA-2111,CARBOSET CR-728, CARBOSET CR-785, CARBOSET CR-761, CARBOSET CR-763,CARBOSET CR-765, CARBOSET CR-715, and CARBOSET GA-4028 (LubrizolCorporation); NEOCRYL A-1110, NEOCRYL A-1131, NEOCRYL A-2091, NEOCRYLA-1127, NEOCRYL XK-96, and NEOCRYL XK-14 (DSM); and BAYHYDROL AH XP2754, BAYHYDROL AH XP 2741, BAYHYDROL A 2427, and BAYHYDROL A2651(Bayer), for example, or a combination of two or more of the above.

The concentration of the resin in the ink jet ink according to theinvention is at least 1 wt. % and preferably lower than 30 wt. %, morepreferably lower than 20 wt. %.

A.2.4. Additives

The aqueous inkjet ink may further comprise a surfactant, a humectant, abiocide, a film-forming agent and a thickener as an additive.

Humectants are preferably incorporated in the inkjet ink to prevent theclogging of nozzles. The prevention is due to its ability to slow downthe evaporation rate of the solvents, especially of the water in theink. The humectant is preferably an organic solvent having a higherboiling point than water. Suitable humectants include triacetin,N-methyl-2-pyrrolidone, glycerol, urea, thiourea, ethylene urea, alkylurea, alkyl thiourea, dialkyl urea and dialkyl thiourea, diols,including ethanediols, propanediols, propanetriols, butanediols,pentanediols, and hexanediols; glycols, including propylene glycol,polypropylene glycol, ethylene glycol, polyethylene glycol, diethyleneglycol, tetraethylene glycol, and mixtures and derivatives thereof. Apreferred humectant is glycerol. The humectant is preferably added tothe liquid formulation in an amount of 0.1 to 20 wt. % based on thetotal weight of the liquid.

Any known surfactant may be used in the inkjet ink of the invention.Preferably a glycol surfactant and/or an acetylene alcohol surfactantcan be used. The use of the acetylene glycol surfactant and/or theacetylene alcohol surfactant further reduces bleeding to improveprinting quality, and also improves the drying property in printing toallow high-speed printing. The acetylene glycol surfactant and/or theacetylene alcohol surfactant is preferably one or more selected from 2,4, 7, 9-tetramethyl-5-decine-4, 7-diol, alkylene oxide adducts of2,4,7,9-tetramethyl-5-decine-4, 7-diol, 2,4-dimethyl-5-decin-4-ol, andalkylene oxide adducts of 2,4-dimethyl-5-decin -4-ol. These areavailable, for example, from Air Products (GB) as Olfine (registeredtrademark) 104 series and E series, such as Olfine E1 010, or fromNissin Chemical Industry as Surfynol (registered trademark) 465 andSurfynol 61.

A biocide may be added to the ink to prevent unwanted microbial growth,which may occur in the liquid. The biocide may be used either singly orin combination. Suitable biocides for the ink-jet ink of the presentinvention include sodium dehydroacetate, 2-phenoxyethanol, sodiumbenzoate, sodium pyridinethion-1-oxide, ethyl p-hydroxybenzoate and1,2-benzisothiazolin -3-one and salts thereof. Preferred biocides areProxel™ GXL and Proxel™ Ultra 5 available from ARCH UK BIOCIDES andBronidox™ available from COGNIS.

A biocide is preferably added to the aqueous medium in an amount of0.001 to 3 wt. %, more preferably 0.01 to 1.0 wt. %, each based on theink liquid.

The inkjet ink may further comprise at least one thickener for viscosityregulation in the liquid. Suitable thickeners include urea or ureaderivatives, hydroxyethylcellulose, carboxymethylcellulose,hydroxypropylcellulose, derived chitin, derived starch, carrageenan,pullulan, proteins, poly(styrenesulphonic acid), poly(styrene-co-maleicanhydride), poly(alkyl vinyl ether-co-maleic anhydride), polyacrylamid,partially hydrolyzed polyacrylamid, poly(acrylic acid), poly(vinylalcohol), partially hydrolyzed poly(vinyl acetate), poly(hydroxyethylacrylate), poly(methyl vinyl ether), polyvinylpyrrolidone,poly(2-vinylpyridine), poly(4-vinylpyridine) andpoly(diallyldimethylammonium chloride).

The thickener is added preferably in an amount of 0.01 to 20 wt. %, morepreferably 0.1 to 10 wt. % based on the ink.

B. Inkjet Recording Method B.1. Application Method of the TreatmentLiquid

The treatment liquid according to the present invention is suitable fortreating different substrates, porous and non-porous ones. Poroussubstrates include paper, card board, white lined chipboard, corrugatedboard, packaging board, wood, ceramics, stone, leather and textile.Non-porous substrates include metal, glass, polypropylene,polyvinylchloride, PET, PMMA, polycarbonate, polyamide, polystyrene orco-polymers thereof. The treatment liquid according to the presentinvention is also suitable for treating jetted images, commonly known aspost treatment fluid.

All well-known conventional methods can be used for coating orimpregnating the treatment liquid on a substrate or on an image formedby jetting an aqueous inkjet ink. Examples of the method include airknife coating, blade coating, roll coating, gravure coating. Afterapplying the treatment liquid onto a substrate, the coating ispreferably dried before printing the image onto the treated substrate.

The treatment liquid is particularly suitable for treating poroussubstrates, before or after printing images with inkjet printing.

The treatment liquid is also suitable for treating textile fabrics. Thetextile fabric used is made of one type of fibre or blended fibre of twoor more selected from the group consisting of cotton, hemp, rayon fibre,acetate fibre, silk, nylon fibre, and polyester fibre. The fabric may bein any form, for example, a woven, knitted, or nonwoven form of theabove-mentioned fibres. The treatment liquid containing the polyurethaneresin according to the invention can be preferably applied to the fabricby spraying, coating, padding or pad printing.

Alternatively, the treatment liquid may also be applied to the substrateusing an ink jet head or valve jet head. This means of applying thetreatment liquid, which is according to an image, has the advantage thatthe amount of required treatment liquid is substantially lower than withthe other application methods. By means of a jetting head, it ispossible to apply treatment liquid onto areas of the substrate where theimage should be printed. Suitable ink jet head types for applying thetreatment liquid are piezoelectric type, continuous type, thermal printhead type or valve jet type.

Substrates to which the treatment liquid has been applied may be driedand optionally undergo a heat treatment, before the subsequent inkjetting step with the colorant containing ink. Examples of the heatingprocess include, but are not limited to, heat press, atmosphericsteaming, high-pressure steaming, and THERMOFIX. Any heat source can beused for the heating process; for example, an infrared ray lamp isemployed.

In another preferred embodiment of the invention, the treatment liquid,after having been applied onto a substrate, is not substantially driedbefore the image is printed by means of the jetting of the aqueous inkjetting step.

B.2. Ink Jetting & Drying

After the application of the treatment liquid to the substrate, theaqueous inkjet ink according to the invention is applied the substrate.The inkjet ink comprises a colorant, more preferably a pigment. Apreferred method of applying the aqueous inkjet ink is by means of anink jetting technique.

A preferred ink jet head for the inkjet printing system is apiezoelectric ink jet head. Piezoelectric inkjet jetting is based on themovement of a piezoelectric ceramic transducer when a voltage is appliedthereto. The application of a voltage changes the shape of thepiezoelectric ceramic transducer in the print head creating a void,which is then filled with ink. When the voltage is again removed, theceramic expands to its original shape, ejecting a drop of ink from theink jet head. However, the jetting of the ink according to the presentinvention is not restricted to piezoelectric inkjet printing. Otherinkjet print heads can be used and include various types, such as acontinuous type, a thermal print head type and a valve jet type.

EXAMPLES Measurement Methods 1. Viscosity

The viscosity of the treatment liquids was measured at 32° C. using a“Robotic Viscometer Type VISCObot” from CAMBRIDGE APPLIED SYSTEMS.

2. Storage Stability

Treatment liquid stability was evaluated numerically and visually. Ifthe relative viscosity of the treatment liquid increases more than 40%after being stored for 2 weeks at 60° C. the treatment liquid is calledunstable. If the treatment liquid solidifies, the treatment liquid iscalled unstable.

Materials

All materials used in the following examples were readily available fromstandard sources such as Sigma-Aldrich (Belgium) and Acros (Belgium)unless otherwise specified. The water used was demineralised water.

-   -   Acetone is acetone p.a. supplied by VWR International    -   Vylon 220 is a polyester polyol containing terephthalic ester        and isophthalic ester units obtained from Toyobo    -   Ymer N120 is 1,3 diol polyether supplied by Perstorp    -   DBTL is dibutyl tin laurate (KEVER-KAT DBTL 162) supplied by        Brenntag    -   IPDI is a Vestanat IPDI, isocyanate supplied by Evonik    -   BD is 1,4-butane diol supplied by Acros    -   Triethylamine is triethylamine supplied by Acros    -   Disperbyk 190 is a 40 wt. % solution of dispersing agent        supplied by BYK CHEMIE GMBH    -   Imagisperse is a TiO₂-dispersion supplied by Imagico

India and available under the trade name Imagisperse Aqua White

-   -   PYR is 2-pyrrolidone.    -   HD is 1,2-hexanediol    -   Proxel K is an aqueous solution of 5-10% 1,2-Benzisothiazolin        -3-one    -   PU-9 is the reproduction of the polyurethane dispersion PU-9,        prepared as disclosed in the unpublished patent application        EP16196224.6 and having a solid content of 41.9 wt. %    -   PU-10 is the reproduction of the polyurethane dispersion PU-9,        prepared as disclosed in the published patent application        EP16196224.6 and having a solid content of 33.8 wt. %    -   COL is a commercial cyan dispersion supplied by Cabot

Corporation, available under the trade name Cab-O-Jet 450 C

-   -   SURF-1 is Capstone FS3100, a surfactant from Dupont    -   SURF-2 is Tego Twin 4000, a surfactant from Evonik Industries    -   SURF-3 is TEGO WET 270    -   SUBSTR-1 is Metamark MD5-100 (PVC)

Preparation of the Polyurethane Resin Dispersions PU-1 (INV)

In an Erlenmeyer of 500 ml the following compounds were weighed: 104.22g of Vylon 220, 15.30 g of Ymer N120 and 201.45 g of acetone. The YmerN120 was preheated in an oven at 80° C., in order to obtain a liquidwhich can be easily handled. The mixture weighed in the Erlenmeyer wasstirred using a magnetic stirrer and heated to 45° C. A clear solutionwas obtained and cooled to room temperature which will be later on usedin the reaction. In a 500 ml 3 necked round bottom flask equipped with acoiled condenser and stirrer, 4.61 g of 3-(Dimethylamino)1,2-propanediol was added. The prepared polyol solution (Vylon 220+YmerN120) was added to 3-(Dimethylamino)-1,2-propanediol present in the 500ml 3 necked round bottom flask. 1.07 g of DBTL was diluted in 9.67 g ofacetone and also added to the polyol mixture. Then the reactor washeated to 55° C. during appr. 35 minutes, allowing the3-(Dimethylamino)-1,2-propanediol to dissolve homogenously. Subsequently34.04 g of IPDI was added dropwise via an addition funnel with pressureequalization arm during 20 minutes. The amount isocyanate added was anexcess towards the hydroxyl amount, ie. NCO/OH=1.53). The reaction wasallowed to take place during 2 hours at 55° C. The isocyanato terminatedprepolymer and free IPDI which was available in excess was then furtherreacted using a diol as chain extender. As diol 4.78 g of BD was used.The reaction mixture was cooled to 40° C., in order to avoid evaporationof acetone. The reaction mixture was then allowed to react overnightduring 20 hours at 40° C. s in order to reach full conversion. Thetertiary amine group in the resin was protonated by adding 2.32 g ofacetic acid to the resin solution.

From the protonated PU solution, 345.17 g (44.03% solids) was weighed ina stainless steel vessel. Subsequently the water based dispersion wasmade using Disperlux equipment adding water during high shear mixing.Under stirring at 900 RPM using a 9 cm diameter dissolver stirrer 282.27g of water was added during 20 minutes to the acidified PU solution. Theacetone in the obtained dispersion was evaporated on a rotaryevaporator. In order to avoid foaming the evaporation was started at alower vacuum. The evaporation was stopped when also water was evaporatedat a pressure of 60 mbars and a 40° C. heating bath. Based on the weightthe concentration was corrected by adding water to 35%. The obtainedPU-dispersion showed an excellent colloidal stability. The exact solidcontent was determined by drying 1 g of solution on an aluminum dish at130° C. during 120 minutes. The solid content obtained was 34.96 wt. %.The measured pH is 5.04. Particle size measurement using Zetasizer: 31nm.

PU-2 (INV)

In an Erlenmeyer of 500 ml the following compounds were weighed: 107.39g of Vylon 220 and 201.45 g of acetone. The Erlenmeyer was stirred usinga magnetic stirrer and heated to 45° C. A clear solution was obtainedand cooled to room temperature which will be later on used in thereaction. In a 500 ml 3 necked round bottom flask equipped with a coiledcondenser and stirrer, 8.95 g of 3-(Dimethylamino)-1,2-propanediol wasadded. The prepared polyol solution (Vylon 220) was added to3-(Dimethylamino) -1,2-propanediol present in the 500 ml 3 necked roundbottom flask. 1.07 g of DBTL was diluted in 9.67 g of acetone and alsoadded to the polyol mixture. Then the reactor was heated to 55° C.during appr. 35 minutes, allowing the 3-(Dimethylamino) -1,2-propanediolto dissolve homogenously. Subsequently 41.82 g of IPDI was addeddropwise via an addition funnel with pressure equalization arm during 20minutes. The amount isocyanate added was an excess towards the hydroxylamount, ie. NCO/OH=1.53). The reaction was allowed to take place during2 hours at 55° C. The isocyanato terminated prepolymer and free IPDIwhich was available in excess was then further reacted using a diol aschain extender. As diol 4.78 g of BD was used. The reaction mixture wascooled to 40° C., in order to avoid evaporation of acetone. The reactionmixture was then allowed to react overnight during 20 hours at 40° C. sin order to reach full conversion. The tertiary amino group in the resinwas protonated by adding 4.51 g of acetic acid to the resin solution.

From the protonated PU solution, 353.87 g (44.50 wt. % solids) wasweighed in a stainless steel vessel. Subsequently the water baseddispersion was made using Disperlux equipment adding water during highshear mixing. Under stirring at 900 RPM using a 9 cm diameter dissolverstirrer 292.48 g of water was added during 20 minutes to the acidifiedPU solution. The acetone in the obtained dispersion was evaporated on arotary evaporator. In order to avoid foaming the evaporation was startedat a lower vacuum. The evaporation was stopped when also water wasevaporated at a pressure of 60 mbars and a 40° C. heating bath. Based onthe weight the concentration was corrected by adding water to 35%. Theobtained PU-dispersion showed an excellent colloidal stability. Theexact solid content was determined by drying 1 g of solution on analuminum dish at 130° C. during 120 minutes. The solid content obtainedwas 38.80 wt. %. The measured pH is 4.90. Particle size measurementusing Zetasizer: 33 nm.

Example 1

This example illustrates the need for a polyurethane resin obtained byreacting a polyester polyol and a polyol containing a cationic group ora precursor of a cationic group such as tertiary amino group in order toassure sufficient storage stability of a treatment liquid and at thesame time preserve excellent physical properties of the dried treatmentliquid. The presence of a polyol containing a cationic group during thereaction implies that this compound is built in the PU-resin.

Preparation of Treatment Liquids

Treatment liquids were prepared by mixing the compounds given inTable 1. All weight percentages are relative to the total weight of theinkjet ink.

TABLE 1 PTL-1 (INV) PTL-2 (INV) Compound Content in wt. % Content in wt.% PU-1 (INV) 85.81 — PU-2 (INV) — 86.71 SURF-1 1.0 1.0 Water To completeto 100% To complete to 100%

Evaluation and Results

All treatment liquids comprising the inventive PU-resins show a goodstorage stability.

Example 2

This example shows that treatment liquids wherein the PU-resin accordingto the invention is combined with white pigments show an excellentstorage stability.

Preparation of a White Pigment Dispersion (WIT-1)

275 g of white pigment (TRONOX CR 834) was added to a mixture of 68.75 gof Disperbyk 190 and 2.2 g of Proxel K in 204.05 g of water under highshear by means of a Disperlux. 200 g 0.4 mm yttrium stabilized zirconiabeads (“high wear resistant zirconia grinding media” from TOSOH Co.) wasadded and the white pigment was milled for 75 minutes in a DynomillResearch Lab at a flow of 4500 t/min. The zirconia beads were removed byfiltration and the dispersion was filtered over a 0.7 μm filter. Thedispersion WIT-1 had an average particle size of 219 nm.

Preparation of the Treatment Liquids PTL-3 and PTL-4

Treatment liquids PTL-3 and PTL-4 were prepared by mixing the compoundsgiven in Table 2. All weight percentages are relative to the totalweight of the liquid.

TABLE 2 PTL-3 PTL-4 Compound Content in wt. % Content in wt. % PU-2(INV) 34.32 34.32 Imagisperse 27.50 — WIT-1 — 22.00 PYR 15.0 15.0 HD15.0 15.0 SURF-1 0.6 0.6 SURF-2 0.2 0.2 Water To complete to 100% Tocomplete to 100%

Both treatment liquids show an excellent storage stability, showing thatthe PU-resins according to the invention can be combined with whitepigments without causing storage stability problems in the treatmentliquid.

Example 3

This example illustrates the fixing power towards colorants of thecationic polyurethane binder in the treatment liquid of the set ofliquid according to the invention.

Preparation of the Treatment Liquids PTL-5 and PTL-6

Treatment liquids PTL-5 and PTL-6 were prepared by mixing the compoundsgiven in Table 3.

All weight percentages are relative to the total weight of the liquid.

TABLE 3 PTL-5 (COMP) PTL-6 (INV) Compound Content in wt. % Content inwt. % PU-2 (INV) — 30.93 PU-9 dispersion 35.6 — PYR 20.0 20.0 HD 20.020.0 SURF-3 0.6 0.6 Water To complete to 100% To complete to 100%

Preparation of the INK-1

A cyan ink INK-1 was prepared by mixing the compounds given in Table 4.All weight percentages are relative to the total weight of the inkjetink.

TABLE 4 INK-1 Compound Content in wt. % PU-9 dispersion 28.64 PYR 20.00HD 20.00 SURF-3 0.60 COL 20.00 Water To complete to 100%

Evaluation and Results

The treatment liquids PTL-2 and PTL-5 were coated by using a 10 μmspiral bar (from Elcometer) with a motorised film applicator Elcometer4340 on a sheet of chrome crusted leather supplied from Conceria NutiIvo S. P. A. (Italy). After drying the coated layer at 60° C. in an ovenfor 5 minutes, the treated substrate sheets were coated a second timeeach with the same treatment liquid PTL-2 and PTL-5. After drying thecoated layer at 60° C. in an oven for 5 minutes, the treated substratesheets were coated with INK-1 by means of the same 10 μm spiral bar. Thecoated samples were dried at 60° C. for 8 minutes.

The cyan optical density of the dried coatings was measured by means ofan eXact apparatus (from X-rite) at ANSI A (no filter (M0)). After themeasurements of the optical densities (D), the samples were stored for 3days in a plastic pocket at room temperature and the optical density wasagain measured. It was observed that the optical density of the coatedsamples (D) was decreased, probably due to migration of the colorants ofthe inkjet ink into the porous substrate. In table 5, the measureddecrease in optical density was summarized.

TABLE 5 Sample no Treatment liquid Inkjet ink ΔD due to storage 1 (COMP)PTL-5 INK-1 −0.24 2 (INV) PTL-6 INK-1 −0.13

From Table 5 it can be seen that the decrease in color density uponstorage is less with the use of the set of liquids according to theinvention (PTL-6+INK-1) than with a set of liquids not according to theinvention.

1-10. (canceled)
 11. A liquid set for inkjet recording comprising: anaqueous treatment liquid including a polyurethane resin obtainable byreacting a polyester polyol, a diol including a quaternary N-atom or atertiary amino group, and a polyisocyanate; and an aqueous inkjet inkincluding a colorant; wherein the quaternary N-atom or the tertiaryamino group is present in a side chain of a carbon chain linking twohydroxyl groups of the diol; and the polyester polyol is obtained byreacting a polyol and an aromatic polycarboxylic acid.
 12. The liquidset according to claim 11, wherein the aromatic polycarboxylic acid isselected from the group consisting of terephthalic acid, isophthalicacid, and a combination thereof.
 13. The liquid set according to claim12, wherein an amount of the isophthalic acid in the polyester polyol isat least 20 mol %.
 14. The liquid set according to claim 11, wherein thecolorant includes a pigment.
 15. The liquid set according to claim 12,wherein the colorant includes a pigment.
 16. The liquid set according toclaim 14, wherein the aqueous treatment liquid includes a white pigment.17. The liquid set according to claim 15, wherein the aqueous treatmentliquid includes a white pigment.
 18. The liquid set according to claim11, wherein a polyether diol is present during the reaction of thepolyester polyol, the diol, and the polyisocyanate.
 19. The liquid setaccording to claim 18, wherein the polyether diol is a compoundaccording to Formula 1:

wherein R1 is methyl or ethyl; R2 is C₁-C₄alkyl; and n represents aninteger from 5 to
 50. 20. An inkjet recording method comprising:providing a substrate and the liquid set according to claim 11; applyingon the substrate, the aqueous treatment liquid of the liquid set;jetting the aqueous inkjet ink of the liquid set on an area of thesubstrate where the aqueous treatment liquid was applied; and drying theaqueous inkjet ink.
 21. The inkjet recording method according to claim20, wherein the aromatic polycarboxylic acid is selected from the groupconsisting of terephthalic acid, isophthalic acid, and a combinationthereof.
 22. The inkjet recording method according to claim 20, whereinthe applying of the aqueous treatment liquid includes ink jetting theaqueous treatment liquid.
 23. The inkjet recording method according toclaim 21, wherein the applying of the aqueous treatment liquid includesink jetting the aqueous treatment liquid.
 24. The inkjet recordingmethod according to claim 20, wherein the applying of the aqueoustreatment liquid includes applying the aqueous treatment liquid to forman image.